Supernatants from activated lymphocytes contain lymphokines which can exert growth inhibitory and cytolytic effects on cells in vitro. Important members of these lymphokines are lymphotoxins (LTs). Serological evidence supports the role of some LTs in cell-mediated cytotoxic reactions in vitro. Furthermore, selective tumoricidal and anti-carcinogenic effects in vitro have been ascribed to LTs. The present proposal will undertake the following: 1. Biochemical characterization of homogeneous human Alpha L LT from lectin-activated normal lymphocytes; 2. Documentation of homogeneity and biochemical charcterization of Alpha H LT from lectin-stimulated normal lymphocytes; 3. Continued development and characterization of antisera and monoclonal antibodies specific for Alpha L and Alpha H LT; 4. In collaboration with Genentech, clone the gene from RPMI-1788 B-lymphoblastoid line coding for Alpha L in yeast; 5. Develop specific, cytotoxic human T-killer lines and T-T hybridomas, and isolated and characterize receptor-bearing, cytotoxic molecules therefrom; 6. Test homogeneous Alpha L and Alpha H LT and recombinant Alpha L for selective tumoricidal effects and ability to colony-inhibit chemical carcinogen-transformed fibroblasts in vitro; 7. Block cell-mediated cytotoxic reactions in vitro with immunological reagents specific for Alpha L and Alpha H LT; 8. Use cDNA probes from 4. to isolate mRNA from cytotoxic T-cell lines and T-T hybridomas.